The present invention relates to a liquid tank to contain liquid fuel or the like for a fuel cell, and a fuel cell provided therewith.
Usually, a fuel cell system, which uses liquid fuel such as methanol or a hydrogen generation auxiliary agent such as water, is internally equipped with a tank to store liquid. In the fuel cell system, in order to estimate a remaining time available for a device connected thereto, it is imperative that a remaining amount of liquid in the tank be accurately detected.
One method available for estimating the remaining liquid amount in the tank, as far as an active fuel cell in which fuel is actively sent in liquid form by use of a pump or the like is concerned, is to count the total number of times the pump has been driven. The fuel in the tank is found by a formula V1−V2×n, where V1 is the inner volume of the tank, V2 is a volume sent in liquid form per one time the pump is driven, and n is the total number of times the pump has been driven.
This method, however, is not applicable to a case where the tank is an exchangeable cartridge, and not applicable inherently to a passive fuel cell which does not use a pump. Further, even in a case of an active fuel cell, this method has a drawback in that an inaccurate result is likely to be produced due to accumulation of measurement errors, unless the volume V2 sent in liquid form per one time the pump is driven is extremely accurate. Methanol used as fuel for DMFCs varies in viscosity depending on the temperature. Therefore, it is difficult to keep the volume V2, sent in liquid form per one time the pump is driven, constant at all times. That is, it has been virtually difficult to know the accurate remaining amount by use of this method.
As another method available for checking the remaining amount of liquid in a tank, for example, Patent Document 1 proposes to provide two parallel plate electrodes in a fuel tank to thereby detect the remaining amount by using capacitance. Additionally, Patent Document 2 proposes a method of finding the liquid volume, in which comb-shaped electrodes opposed to each other are patterned on a printed board to detect a stray capacitance generated between interconnections.